The present invention generally relates to circuit breakers and more particularly, to an electromagnetic circuit breaker having a switching mechanism mounted in an insulating casing.
Circuit breakers are widely used in industrial, residential, and commercial applications to provide protection against damage due to overcurrent conditions in an electrical circuit. The electrical circuit through the circuit breaker can be established and interrupted by manual operation of a switching mechanism. In addition, the electrical circuit through the current breaker is automatically interrupted by an electromagnetic trip mechanism actuated by an overcurrent condition through the circuit breaker.
A conventional circuit breaker 20 of the type described above is shown in FIG. 1 in cross section. The circuit breaker 20 includes a casing 22 having separately formed left and right casing portions 24 and 26. A frame 28 supports therein a switching mechanism 30 which is connected to an operation handle 32 and is held at one side by frame guides 34 and 36, respectively provided at the upper and lower portions of the left casing portion 26. With the frame 28 in this position, the right casing portion 26 is assembled on the left casing portion 24 so that the frame 28 is held at its other side by frame guides 38 and 40, respectively provided at the upper and lower portions of the right casing portion 26. The left and right casing portions 24 and 26 are secured to each other by means of a rivet 42.
The structure of FIG. 1 has a disadvantage in that it is impossible to test the switching performance of the switching mechanism 30 by operating the operation handle 32 before the switching mechanism 30 has been completely assembled into the casing portions 24 and 26 since both casing portion 24 and 26 are required to support the frame 28 and the switch mechanism 30. This results in quality control problems.
FIG. 2 shows another example of a conventional circuit breaker having a casing structure which is different from the example of FIG. 1 in that a support 44 is used instead of the frame 28 of FIG. 12. A switching mechanism 30 is incorporated directly into a left casing portion 24, and then held by the support 44 from the right side in the drawing. Thereafter, a right casing portion 26 is put on the left casing portion 24, and then tightly connected with the latter by a rivet 42. As is the case with the structure of FIG. 1, the switching performance of the structure of FIG. 2 cannot be confirmed before the structure has been completely assembled as a circuit breaker, since the switching mechanism 30 is not completely supported until assembly is completed.
FIG. 3 shows an example of a conventional circuit breaker in which the casing is constituted by separately formed upper and lower casing portions 46 and 48. A switching mechanism 30 and a frame 28 are fixedly attached to the lower casing portion 48 by screws 50. The upper casing portion 46 is then mounted on the lower casing portion 48 and tightly connected with the latter by a rivet 42. This structure, however, is high in cost due to the number and shape of parts thereof, and is bulky due to excessive width.
FIG. 4 shows a further example of a conventional circuit breaker in which the casing is constituted by separately formed upper and lower casing portions 46 and 48 similar to the previous example in FIG. 3. A frame 28 into which a switching mechanism portion 30 has been assembled is inserted into the lower casing portion 48 and disposed in position. Then the upper casing portion 46 is attached to the lower casing portion such that engagement protrusions 52 are made to engage with fixing holes 54 of the upper casing portion 46. Switching mechanism 30 is thus captured and securely positioned by between the upper and lower casing portions 46 and 48. Similar to the examples of FIGS. 1 and 2, the structure of this example has a disadvantage in that the switching performance cannot be checked prior to assembly of the casing portions.